In a conventional vapor-compression refrigerant cycle system provided with a Rankine cycle, a compressor of a vapor-compression refrigerant cycle is used as an expansion device in a case where an energy recovery is performed by the Rankine cycle.
For example, in a vapor-compression refrigerant cycle system with a Rankine cycle described in JP Patent No. 3356449, a single heat exchanger is used to function as an evaporator for absorbing heat from air at the time of a refrigeration cycle to thereby evaporate a refrigerant, and is also used to function as a heater for heating the refrigerant by use of a high-temperature heat source at the time of a Rankine cycle. In the case where the heat exchanger is used as both the heater and the evaporator, respective temperature zones of these two functions differ by far from each other. Thus, when the heat exchanger is configured so as to be adaptable as the evaporator, it becomes difficult for the heat exchanger to effectively recover external waste heat by functioning as the heater.
Generally, a compressor of the vapor-compression refrigerant cycle system is for sucking a gas, such as a gas refrigerant and the like, into an operation chamber by giving mechanical energy thereto from outside, and subsequently, reducing a volume of the operation chamber so as to compress the gas to be discharged. On the other hand, an expansion device is for introducing the gas at high-pressure into an operation chamber, and for expanding the operation chamber by the agency of a pressure of the gas to thereby take out mechanical energy. Accordingly, in order to make use of a compressor of a rotary type such as a scroll type as an expansion device, there is the need for reversing the flow of the refrigerant.
In a vapor-compression refrigerant cycle system described in JP-U 63-92021, however, in a case of operating a compressor device so as to function as a compressor for exhibiting refrigeration capacity as well as in a case of operating the compressor device so as to function as an expansion device for executing an energy recovery, a flow of a refrigerant in a compressor part of the compressor device, is in the same direction. For this reason, the flow of the refrigerant in the compressor part of the compression device in the case of operating the compressor device so as to function as the compressor, is not reversed from that in the case of operating the compressor device so as to function as the expansion device.
Further, in a vapor-compression refrigerant cycle system described in JP patent No. 2540738, a refrigerant inlet as well as a refrigerant outlet of an expansion device (compressor), when an energy recovery is performed, is set on the same side as a refrigerant inlet as well as a refrigerant outlet of the compressor (expansion device) when the vapor-compression refrigerant cycle system is operated to have the refrigeration capacity. Accordingly, in the case of using a scroll type compressor, it is impossible to effectively operate the single compressor so as to function as an expansion device. Therefore, either normal operation of a Rankine cycle or normal operation of the vapor-compression refrigerant cycle cannot be performed in practice.
In addition, in this vapor-compression refrigerant cycle system described in JP patent No. 2540738, a liquid pump is necessary to send refrigerant to a vapor generator. However, in a case where the liquid pump sucks the refrigerant, a pressure at a suction side of the liquid pump is reduced, and the sucked refrigerant is partially boiled and evaporated. In this case, a pump efficiency of the liquid pump is decreased, and cavitation is readily caused in the liquid pump.